<!DOCTYPE html>
<html>

<head>
    <!-- 有一个父div，宽度是100%，父div下面有3个子div，等宽，平分父div宽度 -->
    <meta charset="utf-8">
    <title>本地flex实例</title>
    <style>
        body{
            margin: 0;
        }

        .box {
            background-color: cadetblue;
            border-radius: 3px;

            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
        }

        .item {
            /* min-width: 300px; */
            /* max-width: 599px; */
            width: calc(100%/(100%/300px));
            height: 50px;
            background-color: #3F51B5;
            /* flex: 1 0 0; */
            color: white;
            font-size: 30px;
            border: 1px dashed #f4f4f4;
            text-align: center;
            line-height: 50px;
        }
    </style>
</head>

<body>

    <div class="box">
        <span class="item">1</span>
        <span class="item">2</span>
        <span class="item">3</span>
        <span class="item">4</span>
        <span class="item">5</span>
        <span class="item">6</span>
        <span class="item" style="width: 100%;">7</span>
        <span class="item">8</span>
        <span class="item">9</span>
        <span class="item">10</span>
        <span class="item">11</span>
        <span class="item">12</span>
        <span class="item">13</span>
        <span class="item">14</span>
    </div>

</body>

</html>